Swash plate-type motor

ABSTRACT

On a near-bottom inner surface of a tilt piston cylinder hole, only a limited part that contacts an end of a tilt piston when the tilt piston is tilted by a pressing force from a swash plate is laser-hardened along the circumferential direction of the tilt piston cylinder hole (i.e., a hardened part is formed). In the tilt piston cylinder hole, parts other than a near-opening inner surface and the near-bottom inner surface are not laser-hardened.

BACKGROUND

1. Technical Field

One or more embodiments of the present invention relates to a swash plate-type motor including a swash plate tilted and rotationally switched between two positions, namely a low-speed posture and a high-speed posture.

2. Background Art

There has been a problem of the wearing-off of a tilt piston cylinder hole made through a main body casing of a swash plate-type motor. In this connection, we searched for a conventional technology regarding the prevention of the wearing off of a tilt piston cylinder hole, and found a technology disclosed in Patent Document 1.

According to the technology recited in Patent Document 1, a plurality of rings that are centered on the axis of the tilt piston cylinder hole are formed on an internal part of the tilt piston cylinder hole by using laser light. According to the technology, this enhances the seize resistance and the wear resistance of the sliding surface of the tilt piston cylinder hole.

CITATION LIST Patent Documents

Patent Document 1

Japanese Unexamined Patent Publication No. 2010-24900

SUMMARY

The technology recited in Patent Document 1, however, is problematic in that the laser-hardened circular parts are close to one another. When the laser-hardened parts are close to one another, a part having been laser-hardened is heated again and therefore deteriorated in quality. To prevent this problem, it is necessary to sufficiently cool the part having been laser-hardened, before an adjacent part is laser-hardened. As a result, the hardening process takes time.

One or more embodiments of the invention provide a swash plate-type motor having a tilt piston cylinder hole structure that makes it possible to improve the wear resistance and to shorten the time required for the hardening process.

One or more embodiments of the present invention relates to a swash plate-type motor including: an output shaft provided to be rotatable with respect to a main body casing; a cylinder block engaged with the output shaft; pistons provided in cylinder holes formed in the cylinder block, respectively; a swash plate configured to contact the pistons; a tilt piston configured to change a tilt angle of the swash plate by pressing the swash plate; and a tilt piston cylinder hole formed in the main body casing to slidably support the tilt piston, on a near-bottom inner surface of the tilt piston cylinder hole, a limited part that contacts an end of the tilt piston when the tilt piston is tilted by a pressing force from the swash plate being laser-hardened, and the tilt piston cylinder hole being not laser-hardened except at a near-opening inner surface and the near-bottom inner surface.

According to this arrangement, because a part of the tilt piston cylinder hole where the tilt piston hits hardest is laser-hardened, the wear resistance of the tilt piston cylinder hole is sufficiently improved. On the other hand, because in the tilt piston cylinder hole the parts other than the near-opening inner surface and the near-bottom inner surface are not laser-hardened, the time required for the hardening process is shortened.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that the near-bottom inner surface is laser-hardened in a circumferential direction, and the degree of laser-hardening is gradually increased toward the limited part.

The laser-hardened part swells in a protruding manner. According to the arrangement above, discontinuous parts such as steps are unlikely to be formed on the near-bottom inner surface of the tilt piston cylinder hole in the circumferential direction, and hence the near-bottom inner surface is formed to be a smooth circle in cross section. Furthermore, because the swelling height is low in the parts other than the part of the tilt piston cylinder hole where the tilt piston hits hardest, the fluidity of the oil is maintained in the direction in which the tilt piston slides (i.e., in the axial direction), and hence the wearing-off is restrained.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, on the near-bottom inner surface, an opposing part opposing the limited part is not laser-hardened, whereas parts other than the opposing part are continuously laser-hardened.

On the near-bottom inner surface of the tilt piston cylinder hole, the opposing part opposing the limited part contacting the end of the tilt piston is relatively less susceptible to the wearing-off. According to the arrangement above, because this opposing part is not swelled, the fluidity of the oil is maintained in the direction in which the tilt piston slides (i.e., in the axial direction).

In addition to the above, one or more embodiments of the present invention is preferably arranged such that the entirety of the circumference of the near-bottom inner surface is laser-hardened. According to this arrangement, the wear resistance is improved in the entirety of the circumference of the near-bottom inner surface.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, on the near-bottom inner surface, the degree of laser hardening is gradually increased toward parts which are at equal phase differences in a circumferential direction and include the limited part.

According to this arrangement, protruding parts are formed at equal phase differences on the near-bottom inner surface of the tilt piston cylinder hole in the circumferential direction, to have higher wear resistance than the surrounding parts. The tilt piston is stably supported by these protruding parts.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, on the near-bottom inner surface, two lines are formed along the axial direction only at the limited part by laser hardening.

According to the arrangement above, the end of the tilt piston is facilitated to regularly contact the protruding parts having higher wear resistance. Furthermore, the pressing force is restrained because two protruding parts are formed. As a result, the wear resistance is improved.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, on the near-bottom inner surface, two lines are formed along the circumferential direction only at the limited part by laser hardening.

This makes it possible to widen the laser-hardened range. As a result, the wear resistance is improved.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, the entirety of the circumference of the near-opening inner surface is further laser-hardened.

According to this arrangement, the annular protruding part formed circumferentially on the near-opening inner surface of the tilt piston cylinder hole restrains oil leakage, and hence the lubricity of the tilt piston cylinder hole is improved.

Furthermore, the wear resistance is improved over the entire circumference of the near-opening inner surface.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, on the near-opening inner surface, a part which is diagonally opposite to the limited part, which contacts the end of the tilt piston, is further laser-hardened.

According to this arrangement, because a part of the tilt piston cylinder hole where the tilt piston hits hard is laser-hardened, the wear resistance of the tilt piston cylinder hole is sufficiently improved on the opening side. On the other hand, because only limited parts are laser-hardened as in the present embodiment, the time required for the hardening process is shortened.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, on the near-opening inner surface, two lines are formed by laser hardening only at parts each contacting the end of the tilt piston, along the axial direction.

According to this arrangement, the pressing force is restrained because two protruding parts having high wear resistance are provided. As a result, the wear resistance of the tilt piston cylinder hole is further improved on the opening side.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, on the near-opening inner surface, two lines are formed by laser hardening only at parts each contacting the end of the tilt piston, along the circumferential direction.

According to this arrangement, the range of the hardened area by the laser hardening is widened also on the opening side of the tilt piston cylinder hole. As a result, the wear resistance of the tilt piston cylinder hole is further improved on the opening side.

In addition to the above, one or more embodiments of the present invention is preferably arranged such that, the apex of a part swelled by the laser hardening is processed to be a flat surface.

According to this arrangement, the supporting of the tilt piston by the tilt piston cylinder hole (or the movement of the tilt piston) is further stabilized.

According to the present invention, because the tilt piston cylinder hole is laser-hardened at a part which is hit by the tilt piston hardest, the wear resistance of the tilt piston cylinder hole is sufficiently improved. On the other hand, because parts other than the near-opening inner surface and the near-bottom inner surface are not laser-hardened, the time required for the hardening process is shortened.

BRIEF DESCRIPTION OF DRAWINGS

[0031]

FIG. 1 is a cutaway cross section of a swash plate-type motor according to First Embodiment of the present invention.

FIG. 2(A) is an enlarged view of the tilt piston part of FIG. 1, and shows a tilt piston cylinder hole structure according to First Embodiment.

FIG. 2(B) is an enlarged view of the tilt piston part of FIG. 1, and shows the tilt piston cylinder hole structure according to First Embodiment.

FIG. 3(A) illustrates a tilt piston cylinder hole structure according to Second Embodiment.

FIG. 3(B) illustrates the tilt piston cylinder hole structure according to Second Embodiment.

FIG. 4(A) illustrates a tilt piston cylinder hole structure according to a modification of Second Embodiment.

FIG. 4(B) illustrates the tilt piston cylinder hole structure according to the modification of Second Embodiment.

FIG. 5 illustrates a tilt piston cylinder hole structure of a modification of Second Embodiment.

FIG. 6(A) illustrates a tilt piston cylinder hole structure according to Third Embodiment.

FIG. 6(B) illustrates the tilt piston cylinder hole structure according to Third Embodiment.

FIG. 7(A) illustrates a tilt piston cylinder hole structure according to a modification of Third Embodiment.

FIG. 7(B) illustrates the tilt piston cylinder hole structure according to the modification of Third Embodiment.

FIG. 8(A) illustrates a tilt piston cylinder hole structure according to Fourth Embodiment.

FIG. 8(B) illustrates the tilt piston cylinder hole structure according to Fourth Embodiment.

FIG. 8(C) illustrates the tilt piston cylinder hole structure according to Fourth Embodiment.

FIG. 9(A) illustrates a tilt piston cylinder hole structure according to a modification of Fourth Embodiment.

FIG. 9(B) illustrates the tilt piston cylinder hole structure according to the modification of Fourth Embodiment.

FIG. 9(C) illustrates the tilt piston cylinder hole structure according to the modification of Fourth Embodiment.

FIG. 10(A) illustrates a tilt piston cylinder hole structure according to Fifth Embodiment.

FIG. 10(B) illustrates the tilt piston cylinder hole structure according to Fifth Embodiment.

FIG. 11(A) illustrates a tilt piston cylinder hole structure according to a modification of Fifth Embodiment.

FIG. 11(B) illustrates the tilt piston cylinder hole structure according to the modification of Fifth Embodiment.

FIG. 12(A) illustrates a tilt piston cylinder hole structure according to a modification of Fifth Embodiment.

FIG. 12(B) illustrates the tilt piston cylinder hole structure according to the modification of Fifth Embodiment.

FIG. 13(A) illustrates a tilt piston cylinder hole structure according to a modification of Second Embodiment.

FIG. 13(B) illustrates the tilt piston cylinder hole structure according to the modification of Second Embodiment.

DETAILED DESCRIPTION

The following will describe embodiments of the present invention with reference to figures. While a swash plate-type motor of the present embodiments is used for construction vehicles, the swash plate-type motor is usable not only in construction vehicles but also for various purposes, as a two-speed swash plate-type motor having a tilt piston that allows a swash plate to change between two postures, i.e., a low-speed posture and a high-speed posture, and a tilt piston cylinder hole into which the tilt piston is inserted.

(Structure of Swash Plate-Type Motor)

The swash plate-type motor 1 shown in FIG. 1 is mounted on an unillustrated construction vehicle to drive a crawler-type running gear. This swash plate-type motor 1 is constructed as a variable capacity hydraulic motor switchable in speed between high speed and low speed, and is connected to a speed reducer unit 10 as shown in FIG. 1. As the casing 10 a of the speed reducer unit 10 is rotated by receiving the rotational force from the swash plate-type motor 1, an unillustrated crawler belt is driven via an unillustrated sprocket attached to a flange portion 10 b of the casing 10 a.

As shown in FIG. 1, the swash plate-type motor 1 includes components such as a main body casing 11, an output shaft 12, a cylinder block 13, pistons 15, a swash plate 16, a tilt piston 17, and a tilt piston cylinder hole 18.

The main body casing 11 is constituted by casing blocks 11 a and 11 b. In the internal space 20 formed by the combination of the casing block 11 a and the casing block 11 b, components such as the cylinder block 13 and the swash plate 16 are provided. Furthermore, the casing block 11 a rotatably supports the casing 10 a of the speed reducer unit 10.

The output shaft 12 is rotatably supported by the main body casing 11 and protrudes from the internal space 20 toward the speed reducer unit 10. This output shaft 12 constitutes an input shaft of the speed reducer unit 10.

The cylinder block 13 is provided to surround the output shaft 12 in the internal space 20, and is fixed to the output shaft 12 by, for example, spline connection. In this cylinder block 13 are formed a plurality of cylinder holes 14 that are in parallel to the output shaft 12. These cylinder holes 14 are formed along the circumferential directions of the cylinder block 13.

The pistons 15 are inserted into the respective cylinder holes 14 formed in the cylinder block 13. As pressure oil is supplied from an unillustrated hydraulic pump to each cylinder hole 14 and then exhausted, the piston 15 inserted into each cylinder hole 14 reciprocates.

On the swash plate 16 is formed a slope 16 a, and the pistons 15 contact this slope 16 a. In this regard, at the leading end part of each piston 15 contacting the swash plate 16, a sliding member is swingably attached to the main body of the piston 15 to slide on the slope 16 a. As the pressure oil is supplied to and discharged from each cylinder hole 14 of the cylinder block 13, the piston 15 reciprocates with respect to the cylinder hole 14 while the sliding member thereof slides on the slope 16 a, with the result that the cylinder block 13 is rotated with the pistons 15 and the output shaft 12 fixed to the cylinder block 13 is rotated together with the cylinder block 13.

The swash plate 16 switches its posture between the low-speed posture and the high-speed posture, as the later-described tilt piston 17 is driven. As shown in FIG. 1, when the swash plate 16 takes the low-speed posture, because the amount of pressure oil introduced into the cylinder hole 14 when the piston 15 is maximally projected from the cylinder hole 14 of the cylinder block 13 is larger than the amount when the swash plate 16 takes the high-speed posture (i.e., the cylinder capacity is larger), the swash plate 16 is rotated at a low speed by the pressure oil supplied from an unillustrated hydraulic pump at a predetermined flow rate. On the other hand, as the inclination of the swash plate 16 (slope 16 a) is slightly changed by the later-described tilt piston 17 from the state shown in FIG. 1 toward the direction orthogonal to the output shaft 12, the posture of the swash plate 16 is switched to the high-speed posture. In this high-speed posture, because the amount of pressure oil introduced into the cylinder hole 14 when the piston 15 is maximally projected from the cylinder hole 14 of the cylinder block 13 is smaller than the amount in the low-speed posture (i.e., the cylinder capacity is smaller), the swash plate 16 rotates at a high speed by the pressure oil supplied from the unillustrated hydraulic pump at a predetermined flow rate.

As shown in FIG. 1, in the casing block 11 b of the main body casing 11 is formed a tilt piston cylinder hole 18. Into this tilt piston cylinder hole 18, the tilt piston 17 is inserted. The tilt piston 17 is a cylindrical piston provided for changing the tilt angle of the swash plate 16 by pressing an end portion of the swash plate 16. One end of the tilt piston 17 is recessed, and between this recess and the bottom surface side of the tilt piston cylinder hole 18, a back pressure chamber 24 is formed to receive pressure oil for driving the tilt piston 17. In this back pressure chamber 24 is provided a coil spring 23. At the other end of the tilt piston 17, a ball-shaped swinging unit 22 is formed to be swingably supported with respect to the tilt piston 17. To this swinging unit 22, a contact portion 21 is attached by welding or the like to contact the swash plate 16 on the side opposite to the slope 16 a. The contact portion 21 is always pressed onto the swash plate 16 by the coil spring 23. Alternatively, the swinging unit 22 may be fixed to the tilt piston 17 and the contact portion 21 may not be provided.

In addition to the above, the pressure oil is supplied to the back pressure chamber 24 to drive the tilt piston 17, via oil passages 26 a, 26 b, and 26 c. When the two-speed switching valve 27 is in the state shown in FIG. 1, because the upstream oil passage 26 a to which the pressure oil is supplied is cut off from the downstream oil passage 26 b, the pressure oil is not introduced into the back pressure chamber 24 and hence the tilt piston 17 is in the state shown in FIG. 1. That is to say, the tilt piston 17 in the state above is retracted to the bottom side of the tilt piston cylinder hole 18 so that the swash plate takes the low-speed posture. Note that, when being retracted toward the bottom of the tilt piston cylinder hole 18, the tilt piston 17 is able to be retracted until the tilt piston 17 does not protrude from the opening of the tilt piston cylinder hole 18. On the other hand, when an unillustrated pilot pressure switching valve is switched and the pilot pressure oil is introduced into the pilot pressure port 28, the two-speed switching valve 27 is biased by the pilot pressure, with the result that the oil passage 26 a is connected to the oil passage 26 b via a notch 27 a of the two-speed switching valve 27 a. With this, the pressure oil is introduced into the back pressure chamber 24 via the oil passages 26 a, 26 b, and 26 c so that the tilt piston 17 is biased, and hence the tilt piston 17 moves toward the opening side of the tilt piston cylinder hole 18. As a result, the posture of the swash plate 16 is switched to the high-speed posture. As such, the tilt piston 17 is able to switch the swash plate 16 between two postures, i.e., between the low-speed posture and the high-speed posture.

First Embodiment of Tilt Piston Cylinder Hole Structure

The swash plate-type motor 1 is structured as above. Now, the structure of the tilt piston cylinder hole 18 formed in the casing block 11 b of the main body casing 11 constituting the swash plate-type motor 1 will be described with reference to FIGS. 2(A) and 2(B). It is noted that FIG. 2(B) is an A-A cross section of FIG. 2(A). In FIG. 2(A), the coil spring 23 and the contact portion 21 are not illustrated. In FIG. 2(B), components such as the tilt piston 17 are not illustrated, and only the tilt piston cylinder hole 18 is illustrated (the same applies to FIGS. 3(A) and 3(B) and subsequent figures). The casing block 11 b (main body casing 11) is made of cast iron.

Because the tilt piston 17 is arranged to slide on the internal surface of the tilt piston cylinder hole 18, there is a slight gap between the tilt piston 17 and the tilt piston cylinder hole 18. Furthermore, the tilt piston 17 pushes an end portion of the swash plate 16 to incline the swash plate 16. That is to say, as shown in FIG. 2(A), the tilt piston 17 tilts with respect to the central axis of the tilt piston cylinder hole 18, as the tilt piston 17 is pressed by the swash plate 16. It is noted that, the position of the tilt piston 17 when the swash plate 16 takes the high-speed posture is indicated by the full line, whereas the position of the tilt piston 17 when the swash plate 16 takes the low-speed posture is indicated by the two-dot chain line.

As the laser-formed part is denoted by the reference number 3 in FIGS. 2(A) and 2(B), a limited part of the near-bottom inner surface of the tilt piston cylinder hole 18 formed in the casing block 11 b (main body casing 11), which contacts an end of the tilt piston 17 when the tilt piston 17 is tilted by the pressing force from the swash plate 16, is laser-hardened.

The laser hardening is carried out to harden the surface of a component by applying a high-energy-density laser beam to the surface. There are various types of laser oscillators such as carbon dioxide laser, solid-state laser (YAG laser), and semiconductor laser. The laser-hardened part 3 swells in a protruding manner.

In the present embodiment, only a limited part of the near-bottom inner surface of the tilt piston cylinder hole 18, which contacts an end of the tilt piston 17, is laser-hardened to form a single line along the circumferential direction of the tilt piston cylinder hole 18. More specifically, while the output wattage of the laser is kept constant and the scanning (irradiation) speed is kept constant, a short arc is formed by laser only at the limited part contacting the end of the tilt piston 17. It is noted that, in the tilt piston cylinder hole 18, no other parts are laser-hardened except the near-bottom limited part of the hole 18 contacting the end of the tilt piston 17.

According to the present embodiment, because the part (limited part) of the tilt piston cylinder hole 18 which is hit hardest by the tilt piston 17 is laser-treated and hardened, the wear resistance of the tilt piston cylinder hole 18 is sufficiently improved. In the meanwhile, because no parts other than the aforesaid (limited) part are laser-hardened on the tilt piston cylinder hole 18, the time required for the hardening process is shortened.

Second Embodiment

Now, referring to FIGS. 3(A) and 3(B), the tilt piston cylinder hole structure of the Second Embodiment will be described. FIG. 3(B) is an A-A cross section of FIG. 3(A).

In the same manner as First Embodiment shown in FIGS. 2(A) and 2(B), a limited part of the near-bottom inner surface of the tilt piston cylinder hole 18, which contacts an end of the tilt piston 17, is laser-hardened in the present embodiment. Furthermore, also in the present embodiment, a single line is laser-formed on the near-bottom inner surface of the tilt piston cylinder hole 18 along the circumferential direction of the hole.

In the present embodiment, the degree of laser hardening gradually increases toward the part (limited part) contacting the end of the tilt piston 17. Note that, on the near-bottom inner surface of the tilt piston cylinder hole 18, a part opposing the part (limited part) contacting the end of the tilt piston 17 is not laser-hardened, whereas the parts other than the opposing part are continuously and circumferentially laser-hardened.

More specifically, for example, when the inner surface of the tilt piston cylinder hole 18 is circumferentially scanned (irradiated) by laser, the output wattage of the laser is gradually changed from zero to a predetermined wattage and then from the predetermined wattage to zero, while the scanning is conducted from the opposing part opposing the part (limited part) contacting the end of the tilt piston 17 to form a single circle. As such, the degree of swelling by the laser hardening is gradually changed. In the present embodiment, as shown in FIG. 3(B), the laser hardening is conducted circumferentially on the inner surface of the tilt piston cylinder hole 18, in such a way that the scanning speed of the laser is kept constant but the output wattage is changed to arrange the inner surface of the hardened part 32 to be substantially perfectly circular. It is noted that the output wattage of the laser is arranged to be a predetermined wattage (maximum wattage) at the part (limited part) contacting the end of the tilt piston 17.

In the present embodiment, discontinuous parts such as steps are unlikely to be formed on the near-bottom inner surface of the tilt piston cylinder hole 18 in the circumferential direction, and hence the near-bottom inner surface is formed to be a smooth circle in cross section. Furthermore, because the swelling height is low in the parts other than the part of the tilt piston cylinder hole 18 where the tilt piston 17 hits hardest, the fluidity of the oil is maintained in the direction in which the tilt piston 17 slides (i.e., in the axial direction), and hence the wearing-off is restrained.

In addition to the above, on the near-bottom inner surface of the tilt piston cylinder hole 18, the opposing part opposing the limited part contacting the end of the tilt piston 17 is relatively less susceptible to the wearing-off. According to the present embodiment, because this opposing part is not swelled, the fluidity of the oil is maintained in the direction in which the tilt piston 17 slides (i.e., in the axial direction).

(Modification)

Now, referring to FIGS. 4(A) and 4(B), the following will describe a tilt piston cylinder hole structure of a modification of Second Embodiment. FIG. 4(B) is an A-A cross section of FIG. 4(A).

In Second Embodiment, a non-hardened part where the output wattage of the laser is arranged to be zero is provided. On the other hand, the minimum value of the output wattage of the laser in the present embodiment is not zero. That is to say, the entire circumference of the tilt piston cylinder hole 18 is laser-hardened while gradually increasing the degree of laser hardening toward the part (limited part) contacting the tilt piston 17, to arrange the inner surface of the hardened part 33 to be substantially perfectly circular. This makes it possible to improve the wear resistance across the entirety of the circumference of the near-bottom inner surface contacting the end of the tilt piston 17.

(Modification)

Now, referring to FIG. 5, a tilt piston cylinder hole structure of a modification of Second Embodiment will be described.

In Second Embodiment, the near-bottom inner surface contacting the tilt piston 17 is circularly laser-hardened in the circumferential direction. On the other hand, in the present embodiment, the laser output is changed three times while a single circle is formed by the laser hardening.

More specifically, the inner surface is scanned by laser to form a single circle from an opposing part 18 a which is opposite to the part (limited part) contacting the end of the tilt piston 17. In the same manner as Second Embodiment, the scanning speed of the laser is kept constant and the output wattage is gradually changed. For example, from the opposing part 18 a to the part 18 b, the output wattage of the laser is gradually changed from zero to a predetermined wattage (at the limited part contacting the tilt piston 17) and then from the predetermined wattage to zero. Furthermore, the laser output wattage is changed from the part 18 b to the part 18 c and from the part 18 c to the opposing part 18 a, in the same manner as the change from the opposing part 18 a to the part 18 b.

As such, three hardened parts 34 including the limited part (contacting the tilt piston 17), at which the degree of laser hardening is gradually increased, are formed at equal phase differences circumferentially on the near-bottom inner surface of the tilt piston cylinder hole 18.

According to the present embodiment, three protruding parts 34 a are formed at equal phase differences on the near-bottom inner surface of the tilt piston cylinder hole 18 in the circumferential direction, to have higher wear resistance than the surrounding parts. With these protruding parts 34 a, the tilt piston 17 is securely supported. It is noted that the number of the protruding parts 34 a having higher wear resistance than the surrounding parts may not be three.

It is noted that the hardened parts 34 of the present embodiment may be formed by changing the scanning speed while keeping the output wattage of the laser to be constant. To form a protruding part 34 a higher than the surrounding parts, the scanning speed is slowed down at the part. The frequency of the laser scanning is once (i.e., single scanning) also in this case, and hence the processing time is shortened. Furthermore, a part higher than the surrounding parts can be formed in other embodiments, by changing the scanning speed while keeping the output wattage of the laser to be constant.

Third Embodiment

Now, referring to FIGS. 6(A) and 6(B), a tilt piston cylinder hole structure according to Third Embodiment will be described.

FIG. 6(B) is an A-A cross section of FIG. 6(A).

In the present embodiment, two laser-hardened lines are formed along the axial direction of the tilt piston cylinder hole 18, only at a part of the near-bottom inner surface of the tilt piston cylinder hole 18 contacting an end of the tilt piston 17.

According to the present embodiment, the end of the tilt piston 17 is facilitated to regularly contact the hardened parts 35 having higher wear resistance. Furthermore, because two protruding hardened parts 35 are provided, the pressing force is weakened and the wear resistance is improved. Furthermore, even if it is necessary to sufficiently cool one hardened part 35 having been formed before the other hardened part 35 is formed, the total time required for the hardening process is still reduced because the number of the hardened parts 35 is small.

(Modification)

Now, referring to FIGS. 7(A) and 7(B), a tilt piston cylinder hole structure of a modification of Third Embodiment will be described. FIG. 7(B) is an A-A cross section of FIG. 7(A).

In the present embodiment, two laser-hardened lines (hardened parts 3) are formed in the circumferential direction of the tilt piston cylinder hole 18, only at a part of the near-bottom inner surface of the tilt piston cylinder hole 18 contacting an end of the tilt piston 17.

According to the present embodiment, because a range winder than the piston sliding range on the tilt piston cylinder hole 18 in the axial direction is hardened, the wear resistance of the tilt piston cylinder hole 18 is improved.

Fourth Embodiment

Now, referring to FIGS. 8(A), 8(B), and 8(C), a tilt piston cylinder hole structure of Fourth Embodiment will be described. FIG. 8(B) and FIG. 8(C) are an A-A cross section and a B-B cross section of FIG. 8(A), respectively.

In the present embodiment, not only the near-bottom inner surface of the tilt piston cylinder hole 18 but also the near-opening inner surface of the tilt piston cylinder hole 18 are laser-hardened. As the hardened part is denoted by the reference number 4 in FIGS. 8(A), 8(B), and 8(C), a single laser-hardened line is further formed circumferentially on the near-opening inner surface of the tilt piston cylinder hole 18 contacting the end of the tilt piston 17 on the opening side, with a constant output wattage of the laser and a constant scanning speed. It is noted that, except at a part of the near-opening inner surface and apart of the near-bottom inner surface, the tilt piston cylinder hole 18 is not laser-hardened.

According to the present embodiment, the annular hardened part 4 formed circumferentially on the near-opening inner surface of the tilt piston cylinder hole 18 restrains oil leakage, and hence the lubricity of the tilt piston cylinder hole 18 is improved. Furthermore, the wear resistance is improved over the entire circumference of the near-opening inner surface.

(Modification)

Now, referring to FIGS. 9(A), 9(B), and 9(C), the following will describe a tilt piston cylinder hole structure of a modification of Fourth Embodiment. FIG. 9(B) and FIG. 9(C) are an A-A cross section and a B-B cross section of FIG. 9(A), respectively.

While in the embodiment shown in FIGS. 8(A), (B), and (C) the laser hardening is circumferentially conducted on the near-bottom inner surface of the tilt piston cylinder hole 18, in the present embodiment two laser-hardened lines (hardened parts 35) are formed along the axial direction of the tilt piston cylinder hole 18, on the near-bottom inner surface of the tilt piston cylinder hole 18.

According to the present embodiment, because the fluidity of the oil on the bottom side of the tilt piston cylinder hole 18 is higher than the fluidity in the embodiment shown in FIGS. 8(A), (B), and (C), the lubricity of the tilt piston cylinder hole 18 is further improved.

Fifth Embodiment

Now, referring to FIGS. 10(A) and 10(B), a tilt piston cylinder hole structure of Fifth Embodiment will be described. FIG. 10(B) is an A-A cross section of FIG. 10(A).

In the present embodiment, on the near-opening inner surface of the tilt piston cylinder hole 18, a part which is diagonally opposite to the hardened part 3 and contacts an end of the tilt piston 17 is further laser-hardened (hardened part 42). Note that, in a similar manner as the near-bottom inner surface, only the parts of the near-opening inner surface of the tilt piston 17 each contacting the end of the tilt piston 17 are laser-hardened in the circumferential direction of the tilt piston cylinder hole 18.

In the present embodiment, because the hardened part 42 is formed at a part of the near-opening inner surface hit by the tilt piston 17 hard, the wear resistance is sufficiently improved on the opening side of the tilt piston cylinder hole 18. On the other hand, because only limited parts are laser-hardened as in the present embodiment, the time required for the hardening process is shortened.

(Modification)

The following will describe a tilt piston cylinder hole structure of a modification of Fifth Embodiment, with reference to FIGS. 11(A) and 11(B). FIG. 11(B) is an A-A cross section of FIG. 11(A).

In the present embodiment, on the near-opening inner surface and the near-bottom inner surface of the tilt piston cylinder hole 18, two laser-hardened lines are formed along the axial direction only at parts each contacting the end of the tilt piston 17.

According to the present embodiment, because two protruding hardened parts (35 and 43) having improved wear resistance are provided, the pressing force is restrained and the wear resistance is improved both at the near-bottom inner surface and at the near-opening inner surface.

(Modification)

Now, referring to FIGS. 12(A) and 12(B), a tilt piston cylinder hole structure of a modification of Fifth Embodiment will be described. FIG. 12(B) is an A-A cross section of FIG. 12(A).

In the present embodiment, on the near-opening inner surface and the near-bottom inner surface of the tilt piston cylinder hole 18, two laser-hardened lines are formed along the circumferential direction only at parts each contacting the end of the tilt piston 17. According to the present embodiment, the range of the hardened area by the laser hardening is widened also on the opening side of the tilt piston cylinder hole 18.

(Modification)

Lastly, referring to FIGS. 13(A) and 13(B), a tilt piston cylinder hole structure of a modification of Second Embodiment shown in FIGS. 3(A) and 3(B) will be described. FIG. 13(B) is an A-A cross section of FIG. 13(A).

In the present embodiment, the apex of the hardened part 36 having been swelled on account of the laser hardening is processed to be a flat surface 36 a. The processing may be done by mechanical scraping, squashing of the apex, or the like. In the present embodiment, the supporting of the tilt piston 17 by the tilt piston cylinder hole 18 (or the movement of the tilt piston 17) is further stabilized.

The processing of the apex of the hardened part to be flat may be conducted not only in the tilt piston cylinder hole structure of Second Embodiment show in FIGS. 3(A) and 3(B) but also in the tilt piston cylinder hole structures of all embodiments shown in FIGS. 2(A) and 2(B) and FIGS. 4(A) to 12(B).

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims

REFERENCE SIGNS LIST

-   1: SWASH PLATE-TYPE MOTOR -   11: MAIN BODY CASING -   12: OUTPUT SHAFT -   13: CYLINDER BLOCK -   14: CYLINDER HOLE -   15: PISTON -   16: SWASH PLATE -   17: TILT PISTON -   18: TILT PISTON CYLINDER HOLE 

1. A swash plate-type motor comprising: an output shaft provided to be rotatable with respect to a main body casing; a cylinder block engaged with the output shaft; pistons provided in cylinder holes formed in the cylinder block, respectively; a swash plate configured to contact the pistons; a tilt piston configured to change a tilt angle of the swash plate by pressing the swash plate; and a tilt piston cylinder hole formed in the main body casing to slidably support the tilt piston, on a near-bottom inner surface of the tilt piston cylinder hole, a limited part that contacts an end of the tilt piston when the tilt piston is tilted by a pressing force from the swash plate being laser-hardened, and the tilt piston cylinder hole being not laser-hardened except at a near-opening inner surface and the near-bottom inner surface.
 2. The swash plate-type motor according to claim 1, wherein, the near-bottom inner surface is laser-hardened in a circumferential direction, and a degree of laser-hardening is gradually increased toward the limited part.
 3. The swash plate-type motor according to claim 2, wherein, on the near-bottom inner surface, an opposing part opposing the limited part is not laser hardened, whereas parts other than the opposing part are continuously laser hardened.
 4. The swash plate-type motor according to claim 2, wherein, an entirety of a circumference of the near-bottom inner surface is laser-hardened.
 5. The swash plate-type motor according to claim 3, wherein, on the near-bottom inner surface, the degree of laser hardening is gradually increased toward parts which are at equal phase differences in a circumferential direction and include the limited part.
 6. The swash plate-type motor according to claim 1, wherein, on the near-bottom inner surface, two lines are formed along an axial direction only at the limited part by laser hardening.
 7. The swash plate-type motor according to claim 1, wherein, on the near-bottom inner surface, two lines are formed along a circumferential direction only at the limited part by laser hardening.
 8. The swash plate-type motor according to claim 1, wherein, an entirety of the circumference of the near-opening inner surface is further laser-hardened.
 9. The swash plate-type motor according to any one of claim 1, wherein, on the near-opening inner surface, a part which is diagonally opposite to the limited part, which contacts the end of the tilt piston, is further laser-hardened.
 10. The swash plate-type motor according to claim 9, wherein, on the near-opening inner surface, two lines are formed by laser hardening only at parts each contacting the end of the tilt piston, along an axial direction.
 11. The swash plate-type motor according to claim 9, wherein, on the near-opening inner surface, two lines are formed by laser hardening only at parts each contacting the end of the tilt piston, along a circumferential direction.
 12. The swash plate-type motor according to claim 1, wherein, an apex of a part swelled by the laser hardening is processed to be a flat surface. 